In the production of Filtralite, clay is fed into long rotary kilns. The clay takes a few hours to pass through the rotary kiln, where the clay is dried, pelletised and expanded at temperatures reaching 1200^oC. Expansion takes place when the organic matter stored in the clay combusts and the gas formation generates pores. The expanded clay pellets are then screened, sorted and if required crushed into different gradings according to customers requirements.